While the molecular alterations in infiltrating ductal breast carcinomas are well characterized, little is known about the molecular changes in early breast disease. We plan in situ hybridizations to determine the mRNA expression levels of cell cycle associated genes and growth factor receptor genes in low grade ductal carcinoma in situ (DCIS) and premalignant atypical ductal hyperplasias (ADH) of the human breast. The accuracy, sensitivity and reliability of in situ hybridizations using formalin fixed, paraffin embedded tumor sections has been determined for cyclins A and D, and the EGF receptor, FLG and BEK receptors for FGF, and IGF receptor. Subcloning of riboprobes for additional cyclin and receptor genes is underway. In preliminary experiments, we have observed deregulated and relatively high levels of cyclin A in DCIS specimens. Cyclin A expression was homogenous within DCIS ducts and highest in relatively small lesions, indicating that it may be a very early change in carcinogenesis. These data stand in contrast to the cell cycle dependent expression of cyclin A at the G2-M boundary in many normal cells, and are consistent with a recent hypothesis that cyclin A may be an oncogene. Overexpression of cyclin D, which is normally expressed at the G1-S boundary of the cell cycle and is amplified in some infiltrating ductal carcinomas, has not been observed to date. Our preliminary data indicate that low grade DCI lesions express receptors for multiple growth factors. Consistent expression of the EGF receptor mRNA and FLG-FGF receptor mRNA have been observed. For both receptors, normal ducts have tended to express less mRNA than DCIS within the same section. These data are expected to define the early molecular alterations in breast cancer, which may lead to therapeutic and preventative strategies.